Harmine

uncontrolled hypertension, significant cardiovascular disease

Harmine (in ayahuasca context) produces dose-dependent diastolic blood pressure elevation (+9 mmHg documented in controlled study). Individuals with uncontrolled hypertension, significant cardiovascular disease, or cardiovascular instability should avoid harmine use. Note: BP data is from ayahuasca (harmine+DMT combination), not harmine alone.

Concurrent use of SSRIs (fluoxetine, paroxetine, sertraline, etc.) or SNRIs (venlafaxine, duloxetine) with harmine is absolutely contraindicated due to serotonin syndrome risk. Ribeiro et al. (2026) modeled harmine–SSRI interactions using PBPK and found that fluoxetine and paroxetine substantially increase harmine systemic exposure, compounding serotonergic risk through both pharmacokinetic and pharmacodynamic mechanisms. A washout period appropriate to the SSRI's half-life is required before harmine administration.

Concurrent use of irreversible MAOIs (phenelzine, tranylcypromine, isocarboxazid) with harmine is absolutely contraindicated. Combined MAO-A inhibition can produce dangerously elevated monoamine levels. A washout period of at least two weeks after irreversible MAOI discontinuation is required before harmine administration.

Individuals with hepatic impairment will have reduced CYP2D6 and CYP1A2 metabolic capacity, resulting in substantially elevated harmine systemic exposure. This increases both the magnitude and duration of MAO-A inhibition, raising the risk of adverse effects and drug interactions.

CYP2D6 poor metabolizers (approximately 6-10% of Caucasian populations) will have substantially higher harmine systemic exposure due to reduced metabolic clearance. This represents a pharmacogenetic relative contraindication requiring dose adjustment. CYP2D6 turnover numbers for harmine are among the highest reported for any CYP2D6 substrate, making this polymorphism particularly consequential.

No reproductive safety data are available for harmine. Given harmine's activity as an MAO-A inhibitor and DYRK1A inhibitor — both of which could affect fetal development — use during pregnancy and lactation is absolutely contraindicated as a precautionary measure.

Harmine's MAO-A inhibition dramatically potentiates the effects of co-administered tryptamines by preventing their first-pass metabolism. This is the pharmacological basis of ayahuasca activity. Unpredictable potentiation renders the combination dangerous without careful, individualized dose titration. Tryptamine doses that are safe alone may produce overwhelming or dangerous effects when combined with harmine.

Standard MAOI class contraindication. Concurrent use of sympathomimetic agents (amphetamines, ephedrine, pseudoephedrine, phenylephrine) with harmine may produce exaggerated adrenergic effects due to reduced monoamine metabolism. Risk is lower than with irreversible MAOIs due to competitive displacement, but caution is warranted.

The classic hypertensive 'cheese effect' associated with irreversible MAOIs is substantially reduced with reversible inhibitors like harmine, because dietary tyramine can competitively displace the reversible inhibitor from MAO-A. However, caution with high-tyramine foods (aged cheeses, fermented foods, cured meats) remains advisable at doses producing significant MAO-A inhibition.